I think the solo traveller has always had more options. The problems come when travelling as a couple, buying two PE seats (we are talking holidays not biz) is prohibitive. I can think of three friends who are couple + one small child (under aged 7) for whom this could very well be the ideal solution. Bear in mind that many of NZ's pax are children + grandchild going to visit grandparents.
I have no doubt that NZ know their market and I don't think that it's an idea looking for a solution but very much the solution that many have been looking for. of course, until tried, we cannot know - but it looks well worth a try.